[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to extend 40 yr of prior demographic work on northern elephant seals (Mirounga angustirostris) at Año Nuevo, California, by including the oldest animals. We used a Bayesian mark-recapture analysis to estimate lifelong survival and lifespan of a cohort of 372 weaned pups branded in 1985–1987 and resighted until 2008. Annual survival probability of females averaged 86.3%/yr at ages 5–16, then declined until age 21, the age of the oldest female. Male survival was lower, averaging 67.7%/yr from age 1 to age 15, the age of the oldest male. Northern elephant seal females in the expanding population at Año Nuevo live longer than southern elephant seal females (M. leonina) at colonies whose populations are declining. This comparison suggests that high survival of females is a key factor in population growth.
[Show abstract][Hide abstract] ABSTRACT: Wildlife viewing spectacles that are accessible to the public are immensely popular, raise revenue, contribute to livelihoods, create awareness, and often support conservation. When spectacles are in the commons, they are vulnerable to overuse and ruin. Our aim was to identify best practices that provide access to the animals without disturbing them. Herein, we examine spectacles where thousands of people may view thousands of wild animals at predictable sites and times. We describe the viewing programs at three distinct sites where elephant seals (Mirounga sp.) breed: Ano Nuevo and Piedras Blancas in California, and Peninsula Valdes in Argentina. We compare the viewing operations with respect to mission, resources and accessibility, and the relationship between viewer number and colony growth, and then we report on the quality of the viewing experience. For best practices, we drew on 67 years of summed field research on these animals by both of us and with our familiarity with viewing programs at these sites. We conclude that five practices reduce viewer impact and enhance the viewing experience: (1) restricting visitor numbers and access to the animals; (2) monitoring impact of viewing on the animals and their habitat; (3) encouraging fundamental research of the animals on site; (4) using trained volunteer guides to interpret the attraction when possible; and (5) requiring independent oversight of commercial operations. All wildlife viewing operations could benefit from adherence to these practices when applicable. At their best, wildlife viewing spectacles are a showcase for sound conservation management and provide an inspirational experience that, for many, is akin to visiting the most sacred cultural places of humankind.
[Show abstract][Hide abstract] ABSTRACT: Our aim was to describe changes in ambient water temperature during the course of migration by northern elephant seals (Mirounga angustirostris) and to examine evidence for the seal using abrupt temperature gradients for locating prey. During migration in the post breeding season, the diving patterns of 10 adult females and 7 breeding-age males from Año Nuevo, California, were recorded with time–depth recorders in 1989–1991. Recorded sea surface temperatures declined from 11–13 °C to a low of 3–9 °C as the seals moved north and increased as they returned. Depth of diving was not closely linked to sharp thermal gradients. A thermocline was evident only at the beginning and end of the migration in less than 100 m of water, where less than 2% of diving takes place. There were sex differences in the temperature range at the depths where 75% of diving and foraging occurred, owing in part to habitat separation. The temperatures were lower and the range narrower for females (4.2–5.2 °C at 388–622 m) than for males (5.3–6.0 °C at 179–439 m). We conclude that the northern elephant seal habitat does not provide abrupt changes in temperature that might serve as important cues for locating prey.
Canadian Journal of Zoology 02/2011; 72(4):643-651. DOI:10.1139/z94-087 · 1.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We describe and review the development of the diving and foraging pattern of northern elephant seals, Mirounga angustirostris, during migrations over the first 2 years of life. The diving pattern and migratory tracks of 23 juveniles, 9–27 months of age, from Año Nuevo and Piedras Blancas, California, were recorded with attached time–depth recorders and Argos satellite tags. The seals exhibited a general diving pattern like that of adults, diving deep (373 ± 77 m per dive (mean ± SD)), long (15.2 ± 2.6 min per dive), and continuously (88.7 ± 2.7% of the time submerged while at sea). Level of performance increased with age and experience up to 2 years of age, the end of the fourth migration, when modal diving performance was equal to that of adults. Juveniles migrated north to the waters west of Oregon, Washington, and British Columbia, moving more slowly and not as far as adults. By the third trip to sea, males began to exhibit more flat-bottomed dives than females, a sex difference observed in adults, suggesting that males supplement a diet of pelagic organisms with benthic prey. These data and related observations of elephant seals suggest that the greatest physiological changes enabling an animal to dive occur near the rookery following weaning, before the first trip to sea; transition to a pelagic existence is difficult, as reflected by high mortality during the first migration; improvement of diving skills continues up to 2 years of age; and sex differences in foraging behavior and foraging location, similar to those seen in adults, are evident before the seals reach 2 years of age.
Canadian Journal of Zoology 02/2011; 74(9-9):1632-1644. DOI:10.1139/z96-181 · 1.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Sex ratio theory predictions concerning differential parental investment in offspring by sex were tested on southern elephant seals, Mirounga leonina, breeding at Península Valdés, Argentina. Females invested equally in sons and daughters, as reflected by the similar mass at birth (mean ± 1 S.D.) of 14 males (44.1 ± 6.5 kg) and 14 females (43.4 ± 3.8 kg), and similar mass at weaning of 52 males (131.5 ± 22.4 kg) and 38 females (131.4 ± 18.3 kg). There were also no sex differences in the rate of mass gain during nursing (males = 4.0 ± 0.9 kg/day; females = 3.9 ± 0.8 kg/day), rate of mass loss during the first month of post-weaning fast (males = 0.85 ± 0.19 kg/day; females = 0.92 ± 0.15 kg/day), mean age at weaning (males = 22.3 ± 1.6 days; females = 22.7 ± 1.7 days), and female nursing behaviour. Mother's size accounted for most of the variation in mass of pups at weaning. Mothers ranked as small, medium and large, weaned pups with a mean mass of 102, 130 and 145 kg, respectively. The sex ratio of weanlings did not differ from unity. These data are consistent with Fisher's (1930) sex ratio theory.
[Show abstract][Hide abstract] ABSTRACT: Our aim was to describe the free-ranging diving pattern and to determine the location of foraging of pregnant female southern elephant seals, Mirounga leonina, from Peninsula Valdes, Argentina. This colony is unusual in two respects: it is removed from deep water by a broad shallow shelf (345–630 km wide), and colony numbers have been increasing in recent years in contrast to numbers from other southern hemisphere colonies that are stable or in decline. Microprocessor controlled, geolocation-time-depth recorders were deployed on four females, recording a total of 15,836 dives (270 dive days) during the period February to April, 1992. Departing seals crossed the continental shelf quickly (54–5–62–1 h) and did not show signs of foraging until reaching deep water, due east of the colony in the South Atlantic Ocean. Diving was virtually continuous (93% of the time underwater) with overall mean (±S.D.) rates of 2.5±0.2 dives/h, mean dive durations of 22.8 ± 7.1 min (maximum dive duration = 79 min) with 1.6±0.6min surface intervals between dives, and dive depths of 431±193m (maximum dive depth = 1,072 m). The diving pattern of females from Patagonia is similar to that of seals from colonies where numbers are decreasing (Macquarie stock) or are stable (South Georgia Island). Our subjects did not, however, feed in or south of the Antarctic Polar Front, or in cold waters along the Antarctic coast, where seals from declining or stable colonies forage.
[Show abstract][Hide abstract] ABSTRACT: Resumen: El objetivo de este estudio fue el conocer el comportamiento alimentario de las hembras de lobo fino de Guadalupe, Arctocephalus townsendi. Se obtuvo la localización en el mar de tres hembras adultas y el comportamiento de buceo de una hembra adulta haciendo uso de instrumentos registradores del tiempo de buceo con localización geográfica (GLTDRs). Las hembras se alimentaron en la Corriente de California al sur de la Isla de Guadalupe. La distancia media del viaje redondo fue de 2,375 ± 1,389 km. La distancia a la zona de alimentación fue de 444 ± 151 km. El primer viaje de alimentación fue de 10 ± 4 días. El Segundo viaje de alimentación fue de 19 ± 8 días. Los viajes de alimentación combinados promediaron 14.4 ± 8.3 días, durante los cuales la velocidad del nado fue de 1.9 ± 0.1 m/s. El tiempo de transito comprendió el 47.9%, el tiempo de buceo fue de 36.2%, y el tiempo de descanso el 15.9%. El tiempo de alimentación (tiempo ocupado en la zona de alimentación, que incluye tiempos de tránsito y buceo) fue el 75% de todo el tiempo pasado en el mar. La profundidad promedio alcanzada por una hembra fue de 17 ± 10 m. La duración promedio de los buceos fue de 2.6 ± 1.4 min. El intervalo en superficie entre buceos fue de 2 min. El tiempo de fondo promedio fue de 1.4 min. Los buceos estaban organizados en trenes de buceos; se registraron 23 trenes de buceos, con una duración promedio por tren de buceo de 3:04 ± 2:30 h. El promedio de buceos por tren de buceo fue de 63 ± 60 buceos. La hembra buceó durante la noche y transitó durante el día. Los buceos comenzaron típicamente alrededor de las 2030 h y terminaron alrededor de las 0530 h. El patrón de buceos y la distancia viajada por las hembras lactantes para alimentarse es similar al de otras especies de lobos finos. Palabras clave: Arctocephalus townsendi, Comportamiento de buceo, Isla Guadalupe, Lobo fino de Guadalupe, localización en el mar, México, viajes de alimentación.
Avances en el Estudio de los Mamíferos de México. Vol II, Publicaciones Especiales 01/2008: pages 595-614; Asociación Mexicana de Mastozoología, A.C. Mexico D.F.., ISBN: 978-607-7637-03-5
[Show abstract][Hide abstract] ABSTRACT: Many organisms reproduce in temporary aggregations where estimates of colony size can be made by direct counts. When individuals are not synchronous, however, early breeders depart before the last arrive, so counts underestimate the total breeding population. We present a model describing a colony's census as a function of arrival, breeding tenure, and the correlation between them, and we use it to illustrate how variance in arrival and tenure affect the census. Counts of breeding female northern elephant seals (Mirounga angustirostris) from 1975 to 2007 were used to test the model. Four of the model's parameters—population size, mean and variance of arrival date, and the correlation between arrival date and breeding tenure—could be estimated from census data using a Bayesian approach; prior estimates of two other parameters—mean tenure and its variance—had to be used to avoid overparameterization. The model's predictions fit observed censuses well and produced reliable estimates of population size and arrival behavior, showing that the maximum census was 8%–16% below the total number of breeding females. This method could be used for estimating abundance in any asynchronous aggregation, given independent information on one of the defining distributions: arrival, tenure, or departure.
[Show abstract][Hide abstract] ABSTRACT: We investigated swimming speed, a key variable in both the management of oxygen stores and foraging strategies, and its relationship to diving behaviour in northern elephant seals, Mirounga angustirostris. Swimming speed significantly reduced the dive duration and time at depth for presumed foraging dives, but increased with dive depth. This suggests that the extended duration of deep dives is made possible by physiological adjustments and not by changes in swimming speed or effort. Swimming speeds were similar across sex and age classes despite different predicted minimum cost of transport speeds.All seals exhibited characteristic dive shapes and swimming speed patterns that support their putative functions, but two-dimensional dive shapes and swimming angles varied between sexes and age classes. Mean dive angles on descent were markedly shallow, suggesting use of negative buoyancy to cover horizontal distance while diving. Buoyancy also appeared to affect two-dimensional dive shapes and ability to use extended gliding behaviours between surface and deep foraging zones. Significant differences in diving behaviour between sexes and between young and adult females were evident for various phases of the dive cycle, potentially resulting from physical constraints or differences in dive functionality.
Deep Sea Research Part II Topical Studies in Oceanography 02/2007; 54(3-4):369-383. DOI:10.1016/j.dsr2.2006.12.001 · 2.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Northern elephant seals (Mirounga angustirostris) are characterized by extended fasting during which they rely entirely on their own body reserves. During fasts, lipids are mobilized from blubber to match the energy requirements of the animal. This transfer frees toxic fat-soluble pollutants into the blood circulation, which may exert adverse health effects, especially in young and developing animals. We investigated the dynamics of mobilization of polychlorinated biphenyls (PCBs) from the blubber of northern elephant seal pups during the post-weaning fast. Longitudinal samples of blubber and serum were collected from free-ranging animals throughout the fast at Año Nuevo, California. Blubber biopsies were separated into inner and outer layers. The PCB profiles of blubber and serum consisted mainly of penta- (PCB-101, -110, -118), hexa- (PCB-138, -153) and hepta- (PCB-180, -183, -187) chlorobiphenyls, which accounted for almost 90% of the total PCB burden. Total PCB concentrations in inner blubber increased significantly between early and late fasting (563.6+/-162.0 microg/kg lipids at early versus 911.6+/-513.1 microg/kg lipids at late fasting) whereas they remained fairly constant in outer blubber (572.6+/-134.8 microg/kg lipids at early versus 659.2+/-158.8 microg/kg lipids at late fasting). A corresponding rise of PCB concentrations was observed in serum during the second half of the fast (3.8+/-1.1 microg/l serum at early versus 7.2+/-0.9 microg/l at late fasting). The longitudinal changes in circulating total PCBs could not be explained by the changes in serum lipid fractions (cholesterol, phospholipids, triacylglycerols and free fatty acids). The increases in total PCB concentrations in inner blubber and serum were more pronounced in leaner animals, which suggests that they might be more at risk to potential toxic effects.
[Show abstract][Hide abstract] ABSTRACT: Harbour seals sometimes breed along inland travel corridors where females become clustered in space and time and males establish underwater acoustic display territories similar to terrestrial arenas known as resource-based leks. Under these conditions, we predicted that higher levels of polygyny would be observed than has been previously reported for this species mating in open coast environments without travel corridors. Reproductive success (RS) of 70 males was measured using 20 microsatellite DNA loci and likelihood-based paternity analysis of 136 offspring collected over 3 years. Most males were assigned either zero or one paternity with 80% confidence. The greatest number of pups assigned to one male in a season was two. Variance in RS was higher for males than females (which are biologically limited to one offspring per year) indicating low to mild polygyny. In addition, distributions of relatedness values among pups within year classes did not differ significantly from a simulated distribution with R = 0, indicating that half-siblings were uncommon. Overall, polygyny levels were low relative to terrestrial pinniped mating systems and similar to observations from a harbour seal population along an open coast. Due to large confidence intervals associated with our results, we cannot rule out the hypothesis that a travel corridor might increase the degree of polygyny skew relative to that observed in open coast environments. Habitat appeared to influence male strategies as the most successful males in open coast environments patrolled offshore, while the most successful male in this study defended a territory along the travel corridor.
[Show abstract][Hide abstract] ABSTRACT: Fifty-two male elephant seals were weighed and photographed at Año Nuevo State Reserve, California, to establish a predictive relationship between photographically measured morphological variables (length, side area, and girth area) and body mass. Regression of mass on these variables revealed that side area, roughly equivalent to a longitudinal cross-section, was the most useful single variable for predicting mass, and that adding the other two variables to side area slightly improved the accuracy of the photogrammetric technique. Curvilinear regressions based on a power model provided the best predictive relationships. This technique may prove useful for estimating body mass of other pinnipeds.
[Show abstract][Hide abstract] ABSTRACT: We show that southern elephant seal (Mirounga leonina) colonies existed proximate to the Ross Ice Shelf during the Holocene, well south of their core sub-Antarctic breeding and molting grounds. We propose that this was due to warming (including a previously unrecognized period from approximately 1,100 to 2,300 (14)C yr B.P.) that decreased coastal sea ice and allowed penetration of warmer-than-present climate conditions into the Ross Embayment. If, as proposed in the literature, the ice shelf survived this period, it would have been exposed to environments substantially warmer than present.
Proceedings of the National Academy of Sciences 08/2006; 103(27):10213-7. DOI:10.1073/pnas.0604002103 · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Female northern elephant seals, Mirounga angustirostris, from Año Nuevo (AN) in central California feed offshore in mid-latitude waters (40°–55°N). Migratory patterns and foraging locations of seals from Mexico are unknown. Rookeries on San Benitos (SB) islands in Baja California Sur, Mexico, are ∼1,170 km south of AN. Although the colonies are similar in size, seals from SB begin breeding earlier and have an earlier breeding birthing peak than seals from AN. To determine if the foraging location of seals from Mexico was similar to that of seals from California, we measured δ13C and δ15N values in the hair of 48 suckling pups at SB and 37 from AN, assuming that their isotopic signatures reflected those of mothers' milk, their exclusive diet. The mean δ13C and δ15N values for SB pups (−16.1‰± 0.9‰ and 17.7‰± 0.9‰, respectively) were significantly higher than those for AN pups (−17.6‰± 0.4‰ and 15.6‰± 1.0‰, respectively). From data on environmental isotope gradients and known behavior of SB and AN populations, we hypothesize that the isotope differences are due to females in the SB colony foraging ∼8° south of seals from AN. This hypothesis can be tested by deployment of satellite tags on adult females from the SB colony.
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to measure persistent organic pollutants in northern elephant seals ([NES], Mirounga angustirotris). We obtained blubber biopsy samples from six healthy, newly weaned NES pups from Año Nuevo, California (USA). Contaminant levels were lower than those of other pinnipeds studied on the west coast of North America. Blubber concentrations of polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans averaged 700 +/- 130 microg/kg, 32 +/- 23 ng/kg, and 17 +/- 5 ng/kg (lipid wt), respectively. These contaminants originate from transplacental transfer and from maternal milk, which, in turn, reflect contaminants acquired by the mother from prey during long-distance foraging trips in the northeastern Pacific Ocean. The PCB profile in the blubber of NES pups mainly was composed of penta-, hexa-, and hepta-chlorobiphenyls, possibly reflecting the deep-sea nature of the mother's diet. Our results suggest that NES pups, in contrast to pups of other pinnipeds in the eastern Pacific Ocean, are exposed to low levels of persistent organic pollutants, reflecting an open ocean signal.
[Show abstract][Hide abstract] ABSTRACT: Top-trophic predators like California sea lions bioaccumulate high levels of persistent fat-soluble pollutants that may provoke physiological impairments such as endocrine or vitamins A and E disruption. We measured circulating levels of polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) in 12 healthy juvenile California sea lions captured on Año Nuevo Island, California, in 2002. We investigated the relationship between the contamination by PCBs and DDT and the circulating levels of vitamins A and E and thyroid hormones (thyroxine, T4 and triiodothyronine, T3). Serum concentrations of total PCBs (sigmaPCBs) and total DDT were 14 +/- 9 mg/kg and 28 +/- 19 mg/kg lipid weight, respectively. PCB toxic equivalents (sigmaPCB TEQs) were 320 +/- 170 ng/kg lipid weight. Concentrations of sigmaPCBs and sigmaPCB TEQs in serum lipids were negatively correlated (p < 0.05) with serum vitamin A and T3, potentially reflecting PCB-related toxicity. A slight but not significant negative correlation (p < 0.1) was observed between serum T4 and the levels of sigmaPCBs and sigmaPCB TEQs. Conversely, no relationship was evident between the contaminant concentrations and vitamin E (p > 0.1). As juvenile California sea lions are useful sentinels of coastal contamination, the high levels encountered in their serum is cause for concern about the ecosystem health of the area.